(i) Field of the Invention:
This invention relates to a process for producing chlorine by oxidizing an off-gas, which contains hydrogen chloride gas, with an oxygen-containing gas, and more specifically to a process for producing chlorine by oxidizing an off-gas, which is discharged in the course of preparation of various compounds, with an oxygen-containing gas in a fluidized-bed reactor.
(ii) Description of the Prior Art:
Chlorine is produced on a large scale by electrolysis of brine. In spite of the ever-increasing demand for chlorine, there is a lower demand for caustic soda which occurs simultaneously upon electrolysis of brine. Under the circumstances, it is hence difficult to cope with this imbalance in demand between these compounds.
On the other hand, a great deal of hydrogen chloride is byproduced in reactions of various compounds, for example, chlorination or phosgenation of organic compounds. Because such byproduction of hydrogen chloride is far greater than its market demand, a substantial portion of hydrogen chloride produced as a byproduct is disposed wastefully without its effective utilization. The cost for its disposal has also come up to big figures.
It is hence possible to meet the high demand for chlorine without development of imbalance with the production rate of caustic soda, provided that chlorine can be recovered efficiently from hydrogen chloride which is thrown away in a large volume as described above.
The reaction in which hydrogen chloride is oxidized to produce chlorine has been known as the Deacon reaction for many years. Copper-base catalyst systems, the history of which goes back to the invention of Deacon in 1868, have conventionally been considered to show the best activity. A number of so-called Deacon catalysts, in which various compounds are added as third components to copper chloride and potassium chloride, have been proposed. These catalytic reactions however require elevated temperature of 400.degree. C. and higher and are accompanied by problems in connection with the service life of the respective catalysts.
A variety of proposal has also been made to use chromium oxides as catalysts instead of such Deacon catalyts. None of such chromium oxide catalysts however exhibit sufficient activity. For example, U.K. Pat. Nos. 584,790 and 676,667 disclose to use CrO.sub.3 as a chromia catalyst, in which chromium is trivalent, by having CrO.sub.3 carried on alumina and then calcining it or reducing it with hydrogen. They however disclose low conversions only. These chromium oxide catalysts can provide high initial conversions but their activities drop significantly. As an improvement to the processes disclosed in the above U.K patents, it is also proposed in U.K. Pat. No. 846,832 to mix chromyl chloride in hydrogen chloride as one of the raw materials with a view toward maintaining a high conversion.
As has been described above, chromium oxide catalysts are accompanied by a drawback that their activities decrease when reactions are carried out for long periods of time.